Numerous commercial products are offered for smoke detection in small confined areas, such as rooms, and hallways in a house. They achieve performance according to published guide lines.
These smoke/fire detectors, however, are impractical in large areas with high ceilings, such as auditorium, theater, factory, and aircraft hangar, since these detectors are point sensors and detect smoke only in a small local vicinity to the detector. As a result, large numbers of these detectors are needed.
Installation on high ceilings is difficult. Furthermore, smoke may be dispersed and not reach the height of the ceiling to be detected. Projected and reflected beam smoke detectors, which predict the presence of smoke through measurements of the attenuation of a light beam, are possible solutions. However, in addition to having limited sensitivity, beam-based detectors require precise alignment between the source emitter and the light receiver. Hence such detectors are costly to install and maintain.
There is thus a need for detectors which overcome cost and installation problems associated with known beam-based detectors.